Diurnal Variation of Midlatitiude Thermospheric Zonal Winds during a Period of Low Solar Activity

The seasonal behaviour of thermospheric zonal winds speeds between geomagnetic latitudes 30-40 degrees north and south from 2006 to 2007 has been studied using zonal wind data recently generated from CHAMP measurements using an iterative algorithm. The period, which falls under the declining phase of the recent solar cycle minimum, is characterized by low magnetic activity and low solar flux levels. Seasons are classified into, June solstice, December solstice, March and September equinoxes. No significant differences are observed between north and south mid-latitude wind variation during the equinox seasons. The switch from westward to eastward direction is observed at about 1500 MLT for all the seasons. Large zonal wind speeds are observed at and after dawn in both hemispheres. The significant difference observed in morning winds at the two mid-latitude bands during the solstices may be attributed to the differences in the solar irradiation.